Thanks to a very wet spring in many areas, lots of corn fields are flooded or ponded and could remain that way for sometime. But according to a Purdue Extension agronomist, there are multiple factors that influence whether a corn crop can survive the stress.

"No one can say for sure the day after the storm whether a ponded area of a corn field will survive, or whether there will be long-term yield consequences until enough time has gone by such that you can assess the actual recovery of damaged plants," says Bob Nielsen, corn specialist. "We can, however, talk about the factors that increase or decrease the risks of severe damage or death to flooded fields."

First, plants completely submerged are at higher risk than those partially submerged because those partially submerged may continue photosynthesis at a limited rate.

The amount of time a plant is ponded directly relates to its risk of death. The longer an area remains ponded, the higher the risk of plant death.

"Most agronomists believe young corn can survive up to about 4 days of outright ponding if temperatures are relatively cool — mid-60s or cooler; fewer days if temperatures are in the mid-70s or warmer," Nielsen notes. "Soil oxygen is depleted within about 48 hours of soil saturation. Without oxygen, the plants cannot perform critical life sustaining functions. Nutrient and water uptake are impaired and root growth is inhibited."

Even if surface water subsides quickly, dense surface crusts still can form as the soil dries and can increase the risk of failed emergence for recently planted crops. Nielsen said farmers should be prepared with a rotary hoe to break up the crust and aid emergence.

Factors like mud and old crop residues on plants as water subsides can lead to greater stress on plants because they reduce photosynthesis.

"Ironically, such situations would benefit from another rainfall event to wash the mud deposits from the leaves," Nielsen says.

Corn plants that have yet to reach growth stage V6 — six fully exposed leaf collars — are more susceptible to ponding damage than older plants. This is partially attributed to young plants being more easily submerged than older, taller plants, and partially because the corn plant's growing point is below ground until about growth stage V6, Nielsen explains.

"The health of the growing point can be assessed initially by splitting stalks and looking at the lower portion of the stem," he says. "Within 3-5 days after water drains from the ponded area, look for the appearance of fresh leaves from the whorls of the plants."

Long periods of saturated soils after surface water subsides also can take their toll on a corn crop. This saturation can cause root death, or stunt new root growth until soil moisture returns to a more normal level. Nielsen said corn plants can then be more susceptible to stress and injury during a dry summer because they have restricted root systems.

Along with direct stresses of saturated soils, flooding and ponding can cause significant soil nitrogen loss due to denitrification and leaching.

"Significant loss of soil nitrogen will cause nitrogen deficiencies and possible additional yield loss," Nielsen says. "On the other hand, if corn dies in the ponded areas, it probably doesn't matter how much nitrogen has been lost."

Finally, long periods of wet soil conditions favor development of seedling blight diseases, especially those caused by Pythium fungi, he says. Poorly drained areas of the field are at the highest risk.

Common smut and crazy top also can become greater risks from flooding and cool temperatures.

"The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings," Nielsen says. "The common smut fungal organism is present in soils and can infect young corn plants through tissue damaged by floodwaters. There is limited hybrid resistance to either of these two diseases and predicting damage is difficult until later in the growing season."

More information about the 2011 corn crop is available on Purdue Extension's Corny News Network at:

Source: Purdue University